This application is based on and claims the benefit of German Patent Application No. 10057479.3 filed Nov. 20, 2000, which is incorporated by reference herein.
The invention relates to a method for producing an electrical ribbon cable, wherein at least two bare electrical conductors are arranged in parallel and spaced at a distance from each other between two foils of an insulating material that are firmly joined together while enclosing the conductors and fixing them in position, e.g., as disclosed in Examined German application DE-AS 26 43 838.
Ribbon cables are preferred in wiring technology particularly because of their low height, which is essentially determined only by the conductors. They take up little space and are very simple to install. This is advantageously true particularly if the conductors are flat conductors with a rectangular cross section. The corresponding cables are referred to as flat conductor cables (FCC). Due to their good electrical and mechanical properties and low space requirements, these flat ribbon cables are also used in airbag cassettes for power and signal transmission between fixed and movable parts of motor vehicles.
In all cases, the flat ribbon cablesxe2x80x94hereinafter referred to as xe2x80x9cFCCSxe2x80x9d for short, which should be understood to include all possible variationsxe2x80x94are produced in a laminating process according to the above-cited DE-AS 26 43 838. In a continuous process, for instance two foils of an insulating material provided with an adhesive layer on one side are brought to at least two electrical conductors that are guided in parallel to each other and are joined under pressure while simultaneously being heated. In the finished FCC, the two foils are firmly joined to each other and to the conductors while enclosing the conductors and fixing them in position. This requires a sufficient amount of adhesive applied to the entire width and length of the FCC and determines the production costs of the FCCs to a very substantial degree. The adhesive furthermore contains substances that are toxic and difficult to dispose of.
The object of the invention is to configure the initially described process in such a way that an FCC can be produced at low cost without impairing its mechanical and electrical properties.
According to the invention, this object is attained by ultrasonically welding the two foils together.
This process makes it possible to produce an FCC in a particularly simple and cost effective manner. Two foils of a suitable insulating material simply need to be joined to enclose the conductors, which are guided parallel to each other, and fed to an ultrasonic welding unit in a continuous process. In this ultrasonic welding unit, the foils are welded to each other and, in a preferred embodiment, also to the conductors in order to form a firmly bonded unitxe2x80x94the FCC. In principle, no adhesive is required. This makes it possible significantly to lower the production costs of the FCC. Substances that are difficult to dispose of are not being used.
It may be advantageous to use an adhesion promoter to enhance the ultrasonic coupling. Such an adhesion promoter, which reacts to ultrasound, may be applied prior to welding, for instance to the surface of the conductors and/or as an extremely thin film to at least one of the foils.